Controlled atmosphere chamber

ABSTRACT

Apparatus which permits treatment of products with ultraviolet light in a controlled atmosphere comprises a chamber having inlet and outlet openings for the passage of a product to be treated, one or more ultraviolet light lamps, and at least one gas reservoir within the chamber separated by a foraminous panel. Gas is introduced into the reservoir, passes through the foraminous panel and over and around the path of travel of the workpiece to be treated.

ii. Patent 91 Colem [451 *Oct.30,1973

[ CONTROLLED ATMOSPHERE CHAMBER [75] inventor: George E. Coleman,Elmhurst, Ill.

[73] Assignee: PPG Industries, Inc., Pittsburgh, Pa.

[*1 Notice: The portion of the term of this patent subsequent to April4, 1989 has been disclaimed.

[22] Filed: Jan. 21, 1972 [2]] Appl. No.: 219,681

[52] US. Cl. 250/455 [51] Int. Cl. G0ln 21/00 [58] Field of Search250/43, 49.5 TE,

[56] References Cited I UNITED STATES PATENTS 3,654,459 4 1972 Coleman2594495 TE 7/1954 Nicholls 250/43 3/1959 Wolinski ..250/42 PrimaryExaminer-James W. Lawrence Assistant ExaminerB. C. AndersonAttorneyRussell A. Eberly [57] ABSTRACT Apparatus which permitstreatment of products with ultraviolet light in a controlled atmospherecomprises a chamber having inlet and outlet openings for the passage ofa product to be treated, one or more ultraviolet light lamps, and atleast one gas reservoir within the chamber separated by a foraminouspanel. Gas is introduced into the reservoir, passes through theforaminous panel and over and around the path of travel of the workpieceto be treated.

8 Claims, 3 Drawing Figures CONTROLLED ATMOSPHERE CHAMBER BACKGROUND OFTHE INVENTION Processes in which materials are treated with ultravioletlight to effect polymerization, sterilization, etc. are known in the artand are becoming of increasing importance. The use of ultraviolet lightfor the curing of coatings is also of interest.

The use of ultraviolet light in treating various materials is carriedout by exposing appropriately sensitive materials to light, at leastpart of which has a wavelength in the ultraviolet region. Theultraviolet region is usually considered to extend from about 4,000 A.down to as low as 40 A., although for practical purposes the regionbelow about 2000 A. is not ordinarily significant. While sunlightincludes wavelengths in the ultraviolet region, as received it haslittle or no light at wavelengths much below 3,000 A. due to absorptionby the atmosphere. Thus, for useful processes it is necessary to use anultraviolet lamp.

Several types of lamps are used to produce ultraviolet light. Mercurylamps, in which an electric discharge is passed through mercury vapor,are the most common, but others include metal halide lamps, luminescentor fluorescent lamps, etc. The so-called Sunlamps can also be employed.

It has been found that the efficiency of ultraviolet light in treatingmaterials in many cases depends upon the environment of the materialbeing treated. For example, many materials are more or less sensitive toultraviolet, depending upon the atmosphere in which they are treated.The presence of certain levels of oxygen in the atmosphere is often adetermining factor in both the rate of the desired reaction and thequality of the finished product. Other factors i'nvolve hazards such asthe possibility of fire or explosion and the production of ozone duringthe treatment process.

It is therefore often desirable to carry out treatment with ultravioletlight in a controlled atmosphere in which the level of oxygen can bemaintained within desired limits. While this is relatively easilycarried out in a closed system, most processes cannot be economicallyperformed in closed apparatus and heretofore it has not been possible toprovide efficient control of the atmosphere surrounding a workpiece in aprocess wherein the products treated are continuously or intermittentlymoving.

One proposal for providing an inert atmosphere, sug-' gested for use ina process involving electron beam irradiation, is described in U. S.Pat. No. 2,887,584. The apparatus as described therein comprises achamber open at the bottom into which the product to be irradiated ispassed while attempting to maintain a relatively inert atmosphere insidethe chamber by use of a lighterthan-air inert gas to displace the airtherein. The apparatus as described in the said patent is quite limitedin the extent to which oxygen can be excluded from the path of theproduct to be irradiated, and for this reason does not appear to havebeen successfully utilized.

SUMMARY OF THE INVENTION The apparatus of the present inventioncomprises a chamber having:

A. spaced outer walls with inlet and outlet openings establishing a pathof travel for the workpiece to be treated;

B. at least one ultraviolet lamp positioned over at least a portion ofthe path of travel of the workpiece;

C. at least one foraminous panel within the chamber defining a reservoirbetween the panel and an outer wall of the chamber; and

D. means for introducing gas into the reservoir.

The above-described apparatus provides for treating products withultraviolet light in an atmosphere in which the level of oxygen or anyother gaseous component can be controlled within quite rigid limits. Forexample, where it is desired to exclude oxygen to the extent possible,the present apparatus can easily attain oxygen levels in the path oftravel of a workpiece as low as parts per million or even lower, evenwhere products are being continuously treated and thus are continuouslymoving through the apparatus.

DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a front view of an apparatus comprising one embodiment of theinvention, with a cutaway section showing the interior.

FIG. 2 is a top view of the apparatus of FIG. 1.

FIG. 3 is a perspective view showing the interior of the apparatus andthe top and bottom portions, with a top portion cut awayto show thelamps attached to the inside surface.

Referring to FIGS. 1 and 2, the substantially enclosed chamber 1 isformed by top portion 2, a bottom portion 3, and spacer 18, all mountedon a base 4, in which are installed the required instruments, valves,conveyor drive and electrical source (not shown). Attached to theunderside of top 2 are two ultraviolet lamps 5 and 6, lamp 5 being amercury lamp and lamp 6 being a metal halide lamp. Although only 2 lampsare shown, one or more may be used depending on the energy desired. Thelamps are interchangeably connected to the electrical source throughconnectors 7 and 7. Separating the lamps are reflectors 8, which arecooled by cooling lines 9 which'pass through the reflectors and containcirculating water from water lines 10 and manifold 11. The top of theapparatus is fastened to the bottom 3 during operation by screw clamps12. The bottom 3 has spaced inlet and outlet openings 13 and 13' at theend of extensions 14 and 14. Through these openings passed conveyor 15.A gas manifold 16 is connected to a gas source (not shown) and thisopens through the side wall of bottom 3. Top 2 is shown with a viewingwindow 17 which can be included if desired.

In FIG. 3, the relationship of top 2 and bottom 3 is shown, and there isalso shown spacer 18 which can be placed between the top and bottomportions to vary the enclosed volume if desired. Inside bottom 3 areforaminous panels 19 and 19' forming reservoirs 20 and 20 into which gasis introduced through gas manifolds 16. The top 2 is partially cut awayto show ultraviolet lamps 5 and 6 and reflectors 8, which are attachedto the underside.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus can be of anysuitable size or shape, depending upon the nature of the product orworkpiece to be treated. It is ordinarily rectangular in shape with theultraviolet lamps attached to the upper inside surface. The lampsemployed can be any of the commercially available lamps which emit lightin the ultraviolet region, preferably one which emits predominantly inthe range of 2,000 A. to 3,000 A. Mercury vapor and metal halide vaporlamps are generally utilized. The distance from the lamp to theworkpiece is not ordinarily critical within reasonable limits, and theoptimum distance various with the intensity of the light, the nature andsize of the material treated, the speed with which the workpiece iscarried through the light zone, and similar factors. in the apparatusillustrated, the lamps are located about 1 to 16 inches from theconveyor.

it is not always necessary that the lamps be within the chamber in whichthe workpiece is treated. However, where the lamp is located outside thechamber, a suitable window made of a material which transmitsultraviolet light, such as quartz, should be used so as to permit theultraviolet light to impinge on the desired portion of the path oftravel of the product being treated.

Within the chamber are one or more foraminous panels defining areservoir between an outer wall of the chamber and the panels. Thesepanels can be of varying size and shape, although preferably-rectangularto conform to the cross-section of the chamber. It is preferred that theforaminous panels be oppositely spaced and positioned on each side ofthe path of travel of the product. The holes in the panels should bedistributed more or less uniformly over their surface and should besufficient in size and number to provide a steady and relatively uniformdiffusion of gas into the area of the product.

The volume of the reservoirs is relatively unimportant, except that eachreservoir should be sufficient in volume soas'to reduce turbulence fromthe introduction of gas and to provide a cushioning effect to any gasflow from the gas inlet. The optimum volume of the reservoirs thusdepends upon the number and type of gas inlets, the flow rate of gas,and the overall dimensions of the components of the apparatus. In normaloperation each reservoir acts as a plenum and is at a higher pressurethan the interior of the chamber, thereby maintaining relatively uniformflow through each of the holes in the foraminous panels.

The chamber has openings establishing the path of travel for theproduct. Ordinarily, these openings are in oppositely spaced outer wallsof the chamberand the path of travel passes through the chamber, betweenthe foraminous panels, and beneath the window and the path of theradiation. The cross-sectional area of these inlet and outlet openingsshould be as low as possible to permit the passage of the product, andthe larger the area of the inlet and outlet, the longer the path oftravel through the chamber should be. The object is to provide a stablecondition inside the chamber, thereby minimizing differences due toexternal changes in atmosphere, such as caused by air movements.

it is desirable to provide outwardly extending sections from the outerwalls of the chamber and to locate the inlet and outlet openings inthese extended sections. The extensions are generally of substantiallythe same cross-section as the openings and should extend outwardly for alength sufficient to provide laminar flow of the exit gases from thechamber. The size and shape of the inlet and outlet openings, and theoutwardly extending sections, can be made to conform to the size andshape of various workpieces. Replaceable or movable sections havingdifferent configurations can be provided if desired.

The apparatus also comprises means for the introduction of gas into thereservoir or reservoirs. in order to assist in providing a non-turbulentatmosphere, this is usually accomplished by providing a gas inlet into amanifold, from which the gas passes into the reservoir through aplurality of openings. The gas inlets are usually spaced so as to avoiddirect flow from them into the openings.

As indicated, the overall size of the apparatus can be varied, althoughit can be noted that the overall distance the light must travel beforemeeting the surface of the workpiece affects to some extent thedistribution of energy in the product treated. The apparatus can beconstructed of any material which is not overly sensitive to ultravioletlight, i.e., which does not substantially degrade and become unusablewhen subjected to such light over a period of time. Most metals, glass,plastics, etc., can be used. It is preferred that a noncorrosivematerial be utilized and stainless steel is the specifically preferredmaterial of construction.

The apparatus can also be provided with certain optional components.Reflectors, preferably cooled, can be provided for the lamps. Means forconveying the product along the path of travel can be included, forexample, rollers located in the lower portion of the chamber; these canbe power-driven if desired.

Other auxiliary equipment which is often desirable include means forintroducing gas at the inlet and outlet; these can be gas distributiontubes extending along the opening and having a plurality of inlet holesspaced along their length with the gas flow directed downward,preferably at a 45 angle. Still other optional features includeprovision for continuously or periodically analyzing the atmosphereinside the chamber, means for viewing the interior of the chamber andthe product, such as a transparent window, vacuum or other pumps, andthe like.

The apparatus can be varied in structure to meet the needs of specificprocesses in which it is employed. For example, the apparatus can beused with more than one source of ultraviolet light by providing aplurality of lamps as required. Both sides of a workpiece can beexposed, if desired, or a workpiece'of complex shape can be treated fromvarious angles.

in one embodiment of the invention, an apparatus as shown in thedrawings comprises a chamber 18 inches long and 18 inches wide, with thedepth varying from 3 inches to 18 inches. Attached to the top innersurface are two ultraviolet lamps, each 12 inches long, one a Sylvaniamercury vapor lamp rated at 330 watts/inch and the other a Sylvaniametal halide seeded mercury vapor lamp rated at 330 watts/inch. Thelamps are arranged so that either or both can be used at any one time.Covering each lamp is a polished steel reflector, each reflector havingtherein a coil through which cooling water is circulated when the lampsare in-operation.

The lamps are spaced from "Vs inch to 16 inches from the conveyor whichpasses beneath the lamps and through the chamber, depending upon thespacer employed. Two foraminous panels having 1/16 inch holes uniformlyspaced one-sixteenth inch apart over their entire surface extend alongthe length of the chamber, one on each side, spaced three-fourths inchfrom the outer wall, and rising 2% inches from the bottom. Each of theinlet and outlet openings in the chamber is 14 inches wide by 1 inchhigh, and each is located in a section of the chamber extendingoutwardly 22 inches from opposite chamber walls. A manifold having 6openings each three-fourths inch in diameter opens into each of thereservoirs behind the foraminous panels, each manifold being connectedto a source of nitrogen gas.

The apparatus as described is constructed of stainless steel and canaccommodate products up to about 12 inches wide and about seven-eighthsinch thick. The apparatus can, of course, be made of any size desired,for example, to accommodate panels of 4 or 5 feet in width.

in one example of the manner in which the abovedescribed apparatus isoperated, a total nitrogen flow of 40 cubic feet per minute is passedinto the manifold, distributed into the reservoirs, and passed throughthe foraminous panels into the path of travel of the workpiece. Aproduct line 12 inches wide is carried through the chamber at a rate of50 feet per minute. During such operation, the concentration of oxygenin the path of travel of the product is less than 50 parts per million.if the product line is carried through the chamber at 300 feet perminute, the oxygen content is still maintained below 125 parts permillion.

The apparatus can also be used to provide a sustained level of oxygen(or other gas) during operation. This is desirable using some coatingmaterials, for example, and is accomplished by feeding a controlledmixture of oxygen and nitrogen through the gas distribution system. Anadvantage of the use of the apparatus in this manner is that ozone andother gaseous by-products are removed during operation and thus theconcentration of such by-products does not build up to undesirably highlevels. The apparatus can also be operated at reduced pressure, byproviding suitable auxiliary equipment, e.g., pumps, chambers, etc.

According to the provisions of the patent statutes, there are describedabove the invention and what are now considered to be its bestembodiments. However, within the scope of the appended claims, it is tobe understood that the invention can be practiced otherwise than asspecifically described.

I claim:

1. Apparatus for treating products with ultraviolet light in acontrolled atmosphere, said apparatus comprising a substantiallyenclosed chamber having A. spaced outer walls with spaced inlet andoutlet openings establishing a path of travel for a workpiece,

B. at least one ultraviolet lamp positioned over at least a portion ofsaid path of travel;

C. at least one foraminous panel within said chamber defining areservoir between the panel and an outer wall of the chamber; and

D. means for introducing gas into said reservoir.

2. The apparatus of claim l in which said inlet and outlet openings arelocated in outwardly extending sections of said outer walls.

3. The apparatus of claim 1 in which said foraminous panel hassubstantially uniform openings spaced over its entire surface.

4. The apparatus of claim 1 in which said means for introducing gascomprises a plurality of gas inlet openings into said reservoir.

5. Apparatus for treating products with ultraviolet light in acontrolled atmosphere, said apparatus comprising a substantiallyenclosed chamber having A. oppositely spaced outer walls with spacedinlet and outlet openings establishing a path of travel for a workpiece;

B. at least one ultraviolet lamp positioned over at least a portion ofsaid path of travel;

C. oppositely spaced foraminous panels along each side of said path oftravel, each of said panels defining a reservoir between the panel andan outer wall of the chamber; and

D. means for introducing gas into said reservoirs.

6. The apparatus of claim 5 in which said inlet and outlet openings arelocated in outwardly extending sections of said outer walls.

7. The apparatus of claim 5 in which said foraminous panels havesubstantially uniform openings spaced over their entire surfaces.

8. The apparatus of claim 5 in which said means for introducing gascomprises a plurality of gas inlet openings into each of saidreservoirs.

1. Apparatus for treating products with ultraviolet light in acontrolled atmosphere, said apparatus comprising a substantiallyenclosed chamber having A. spaced outer walls with spaced inlet andoutlet openings establishing a path of travel for a workpiece, B. atleast one ultraviolet lamp positioned over at least a portion of saidpath of travel; C. at least one foraminous panel within said chamberdefining a reservoir between the panel and an outer wall of the chamber;and D. means for introducing gas into said reservoir.
 2. The apparatusof claim 1 in which said inlet and outlet openings are located inoutwardly extending sections of said outer walls.
 3. The apparatus ofclaim 1 in which said foraminous panel has substantially uniformopenings spaced over its entire surface.
 4. The apparatus of claim 1 inwhich said means for introducing gas comprises a plurality of gas inletopenings into said reservoir.
 5. Apparatus for treating products withultraviolet light in a controlled atmosphere, said apparatus comprisinga substantially enclosed chamber having A. oppositely spaced outer wallswith spaced inlet and outlet openings establishing a path of travel fora workpiece; B. at least one ultraviolet lamp positioned over at least aportion of said path of travel; C. oppositely spaced foraminous panelsalong each side of said path of travel, each of said panels defining areservoir between the panel and an outer wall of the chamber; and D.means for introducing gas into said reservoirs.
 6. The apparatus ofclaim 5 in which said inlet and outlet openings are located in outwardlyextending sections of said outer walls.
 7. The apparatus of claim 5 inwhich said foraminous panels have substantially uniform openings spacedover their entire surfaces.
 8. The apparatus of claim 5 in which saidmeans for introducing gas comprises a plurality of gas inlet openingsinto each of said reservoirs.